1. Field of the Invention
This invention relates to a thin film magnetic head, a magnetic head device and a magnetic recording/reproducing device.
2. Related Art Statement
In a magnetic recording field, a thin film magnetic head having a spin-valve film (hereinafter, called as a “SV film”) or a ferromagnetic tunnel junction film (hereinafter, called as a “TMR film”) as a reading element is mainly employed for developing the recording density and the miniaturization.
In such a thin film magnetic head, the reading element includes a second ferromagnetic layer (pinned layer) of which the magnetization is fixed and a first ferromagnetic layer (free layer) of which the magnetization is rotated freely commensurate with an external magnetic field. The resistance of the reading element is minimized as the direction of the magnetization of the second ferromagnetic layer (pinned layer) is parallel to that of the first ferromagnetic layer (free layer), and is maximized as the direction of the magnetization of the second ferromagnetic layer (pinned layer) is anti-parallel to that of the first ferromagnetic layer (free layer). Therefore, a given external magnetic field is detected by measuring the change in resistance as the first ferromagnetic layer (free layer) is rotated. A perpendicular biasing magnetic field is applied to the first ferromagnetic layer (free layer) from a magnetic domain-controlling film to be made single domain, so that Barkhausen noise due to the movement of magnetic wall can be prevented.
The magnetic domain-controlling film may be made of a given antiferromagnetic film. In this case, the perpendicular biasing magnetic field is applied through the bonding with exchange interaction between the antiferromagnetic film and the ferromagnetic film (free layer). Moreover, the magnetic domain-controlling film may be made of a hard magnetic film. In this case, the perpendicular biasing magnetic field is applied from the hard magnetic film. The former biasing means is called as exchange biasing method, and the latter biasing means is called as hard magnetic biasing method.
At both edges of the magnetoresistive effective film in the track width direction are connected a pair of electrode films to flow a sense current therein.
In the above-mentioned conventional thin film magnetic head, normally, the magnetoresistive effective film, the magnetic domain-controlling film and the electrode films are etched and formed by means of ion milling or another dry etching at the same time. Therefore, the depths of the magnetoresistive effective film, the magnetic domain-controlling film and the electrode films are set to almost the same value, as viewed from the direction perpendicular to the track width direction.
If the depth the magnetic domain-controlling film is set to the depth of the magnetoresistive effective film, the perpendicular biasing magnetic field can be uniformly applied to the magnetoresistive effective film to prevent the Barkhausen noise effectively, so that the signal-to-noise ratio (S/N ratio) can be enhanced.
In the above case, however, the sense current is concentrated at the boundaries between the electrode films and the magnetoresistive effective film, so that the electric resistance is increased, which is called as crowding resistance.
When the crowding resistance is increased, the leading resistance is also increased, so that the S/N ratio may be decreased. If the depth dimension of the thin film magnetic head is decreased with the high density recording and the reduction of the track width, the crowding resistance and thus, the leading resistance are remarkably increased, so that the S/N ratio is conspicuously decreased.